A Statistical Design Approach on Electrochemical Impedance Spectroscopy of NMC Li-Ion Battery

Robust development of energy storage materials requires a deep understanding of the relationship between the operation conditions and electrochemical properties. The influences of cell potential and environmental temperature on battery dynamics of commercially available LiNiMnCoO2(NMC)/graphite(C) coin cells were statistically investigated and discussed by using electrochemical impedance spectroscopy measurements and Taguchi statistical design. The Taguchi method reduced the variation in the electrochemical process with an experimental design; therefore, number and duration of impedance measurements were minimized. This design tested three levels for each categorical factor that are the cell potential and the cell temperature. The third level of both potential and temperature optimized the dynamic parameters of the batteries. The calculated signal-to-noise ratio and delta values for the cell temperature were higher for each battery resistance than that of the cell potential. In addition, the calculated probability, P value, was also lower (around zero) for the cell temperature. Thus, the temperature was determined to be the most significant factor, suggesting that this factor should be constrained carefully when the battery dynamics is desired to be optimized. In this paper, the electrochemical impedance spectroscopy method combined with the Taguchi design was performed to offer an unprecedented insight into the effects of the factors on the elements of the equivalent circuit model of the Li-ion coin cells.